US 2500533 A
Description (OCR text may contain errors)
Patented Mar. 14, 1950 PREPARATION OF SOLID HYDROCARBON S Alvin H. Friedman, Bartlesville, kla., assignor to Phillips Petroleum Company, a corporation of Delaware N0 Drawing. Application September 6, 1946, Serial No. 695,305
The present invention relates to the synthesis of hydrocarbons by the catalytic conversion of gaseous mixtures comprising carbon monoxide and hydrogen. In a more particular aspect it relates to an improved method for obtaining an increased yield of solid hydrocarbons in such a conversion.
When carbon monoxide is reacted with hydrogen in the presence of cobalt, nickel, iron and other catalysts, as in a Fischer-Tropsch type process, at somewhat elevated pressures and temperatures of the order of about 100 pounds per square inch and 200 C., the reaction eflluent comprises a complex mixture of solid, liquid and gaseous hydrocarbons. The normally gaseous fraction of various useful materials such as those obtained by oxidation, cracking or dehydrogenation. It is, therefore, frequently desirable to obtain increased yields of wax in a process of the type described. Fischer and Pichler in U. S. Patent 2,206,500 have disclosed increasing the yield of wax from a Fischer-Tropsch process by using a vertical catalytic reactor from which normally solid hydrocarbons which are liquid under the reaction conditions continuously drain. However, this process does not describe any means for regulating the reaction conditions so as to produce a greater proportion of wax within the reaction itself.
It is therefore, an object of the present invention to obtain an increased yield of normally solid hydrocarbons by the synthetic conversion of carbon monoxide-hydrogen mixtures. It is a further object of the present invention to effect the preparation of hydrocarbon waxes by the synthetic conversion of carbon monoxide and hydrogen in the presence of a Fischer-Tropsch type expected from a knowledge of the prior art, when the carbon monoxide-hydrogen feed to a Fischer- Tropsch conversion contains more than 40% of an inert diluent, unusually high yields. of normally solid hydrocarbons are obtained. In addition the yield of gasoline is as high as that obtained from feeds which contain little or no ,diluent, and furthermore, the resultant gasoline contains a higher proportion of olefinic material than gasoline which is obtained by the conversion of diluent free feeds.
According to the prior art the incorporation of up to 40% of nitrogen in the feed will increase the proportion of relatively low-boiling compounds. (Ellis, Chemistry of Petroleum Derivatives, vol. 2, page 1236.) This effect is predictable from the teachings of Craxford (Trans. Faraday Soc., vol. 35, pages 946-958 and pages 966 967, (1939)), Storch (Industrial Engineering Chemistry, line 37, page 340, (1945) and Tsuneoka et al. (Journal of Society of Chemical Industry, vol. 3'7, SupplementalBinding, pages 704- 711 (1934)).
In accordance with the present invention, the feed gas to the Fischer-Tropsch conversion unit and which contains carbon monoxide and hydrogen in a mol ratio of about 1:2, is diluted with a sufllcient amount of an inert diluent such as nitrogen, methane or CO2, to provide a composition containing more than 40% of the diluent and preferably from about 42 to 70% of such diluent. A suitable compositionof feed gas is approximately as follows: 50 volume per cent nitrogen, 16 volume per cent carbon monoxide, and 34 volume per cent hydrogen. Such a feed gas may be prepared by adding the desired proportion of nitrogen to a carbon monoxide-hydrogen mixture prepared by any of the methods known to the art. One especially convenient method for preparing feed gas for use in the process of this invention is by partial combustion of methane with air in the presence of anickel catalyst. The eflluent gas from such a combustion step contains approximately 40 volume per cent nitrogen as well as carbon monoxide and hydrogen in a mol ratio of about 1:2. This efiluent gas may be converted to hydrocarbons without further adjustment of composition, but, preferably, sufiicient nitrogen is added to give a nitrogen content of approximately 42-70 per cent by volume.
The feed is then passed to a reactor, or series of reactors, in the presence of a catalyst suitable for conversion of carbon monoxide and hydrogen to have discovered that contrary to what might be hydrocarbons. In practicing this invention, I
prefer to use a cobalt-containing catalyst such as one consisting of metallic cobalt, thoria, and kieselguhr in the ratio of 100:18z100 parts by weight, respectively. When this catalyst is used, suitable reaction conditions are: pressure, about 100 p. s. i.; temperature, about 200 0.; space velocity, 100 to 200 volumes per volume of catalyst per hour.
Other cobalt-containing catalysts may be used such as cobalt alone or cobalt-nickel-alumina and the like on various supports. In general with cobalt catalysts reaction temperatures in the range of about'175 to 225 C. may be used at pressures of atmospheric to 150 atmospheres or higher and preferably to atmospheres. Other metallic Fischer-Tropsch type catalysts may be used, but cobalt has been found to give preferred results.
The reactor may be one of any of the types known to the Fischer-Tropsch art, but is preferably of the vertical type, since, from this type of reactor, the wax formed may be continuously drained. The reactor is preferably provided with suitable cooling means for temperature control.
The efiluent from the conversion step is treated by customary methods, such as fractional distillation, to separate the various components as desired.
Example Four carbon monoxide-hydrogen feeds containing different proportions of nitrogen were passed through a reactor containing a catalyst consisting of metallic cobalt, thoria, and kieselguhr in the weight ratio 100:18z100. In each feed, the mo] ratio of carbon monoxide to hydrogen was 1:2. The reaction temperature was 200 C., and the pressure was 100 p. s. 1. Other operating data were as follows:
Volume Percent Wax in Gasoline- Free Residue S e Ve ocity, vol./vol./hr.
N2 in Feed,
vol. percent Run m cease rial boiling above 400 F. were obtained in all five runs. Substantially the same volume of gasoline boiling material was obtained in run 4 as in runs l and 5 but this gasoline on analysis was found to be much higher in olefinic content than in runs 1 to 3 and 5. With a diluent concentration below about 42%, the yield of wax is substantially smaller than that which is obtained within the range of about 42% to of diluent in the feed. For example, a 20% increase in N: concentration of from 10% to 30% in the feed caused only a 25% increase in wax concentration (from 20% to 25% in the gasoline-free residue). On the other hand when the Na concentration was increased from 30% to 50%, a increase in wax concentration resulted (from 25% to 50% in the gasoline-free residue).
70% N2 is selected as an upper limit, since this represents. an economic limit beyond which the total yield based on C0 consumed begins to decrease, while the quantity of N2 required to be compressed and recycled becomes excessive for practical operation. With a decrease in yield, the wax production based on C0 reacted also declines beyond this point.
1. A process for the production of wax in high yields which comprises reacting a gaseous mixture containing carbon monoxide and hydrogen in a mol ratio of 1:2 and containing about 50 per cent nitrogen by volume in the presence of a cobalt synthesis catalyst at a temperature with-: in the range of 1'75 to 225 C. and a pressure of from 5 to 15 atmospheres, at a space velocity of from 100 to 200 volumes gas per volume catalyst per hour, and treating the eiiiuents of the reaction to recover therefrom a high yield of wax as a product of the process.
2. A process according to claim 1 wherein the temperature is 200.
3. A process according to claim 1 wherein the temperature is 200 C. and the pressure is 100 pounds per square inch.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,248,099 Linckh et a1 July 8, 1941 2,351,345 Kleine June 13, 1944 FOREIGN PATENTS Number Country Date 500,950 Great Britain Spec. accepted Feb. 17, 1939 510,513 Great Britain Spec. accepted Aug. 2, 1949